1. Field of the Invention
The present invention generally relates to hydraulic shock absorbers used to dampen relative motion between a vehicle body and a vehicle wheel. More particularly, the present invention relates to such shock absorbers featuring a gas chamber and a pair of fluid chambers in which the piston is spring-biased.
2. Description of the Related Art
In conventional hydraulic shock absorbers for vehicular applications, a piston is positioned within a cylinder. A piston rod that is coupled to the piston projects from one end of the cylinder. The hydraulic shock absorber is connected to the wheel and the vehicle body at opposing ends. Typically, the connection locations comprise a rubberized portion (see JP-A-Hei 5-60166, for example).
As is known, the piston is formed with multiple communication passages that allow for fluid to flow from one chamber to another chamber through the piston. The fluid flow is controlled to provide the desired degree of damping. In other words, damping force is generated as the hydraulic shock absorber for a vehicle is extended or contracted due to movement of the hydraulic fluid from one fluid chamber to the other through the communication passages formed in the piston.
Of course, one fluid chamber will have a smaller volumetric change during movement because the piston rod is positioned within that chamber. In other words, as the piston moves down, the volume of the chamber occupied by the piston rod increases, which decreases the amount of fluid that can flow into that chamber. In order to accommodate the difference in volumes, the other chamber has a moveable wall defined by a free piston. The free piston typically separates the other chamber from a gas chamber. The gas chamber is commonly filled with high pressure gas such that the free piston is biased by high-pressure gas (see JP-A-2001-317582, for example).
Conventional hydraulic shock absorbers have a bump stop that is positioned between the cylinder end and the piston, as disclosed for example in JP-U-Hei 5-22885 and JP-A-Hei 10-141421. The bump stop is designed to prevent the piston from colliding with the cylinder in a fully extended position. The bump stop typically is formed of rubber, a compression coil spring, or the like. The bump stop is not in contact with the piston during normal use and is compressed between the cylinder body and the piston during extreme extension of the shock absorber.